Ashton:
Now I just need to determine why the serial LCD displays I have (with terminals GND, VCC, SDA, SCL) are not displaying the serial output of the UNO board when tested. LCD display under test -> http://www.ebay.com/itm/200764158676
That's an I2C/TWI serial LCD. The TinkerKit library is for an LCD connected through the serial port. You will need to download a matching I2C LCD library. The PCF8574T chip on the board connected to the LCD is an I2C 8-bit I/O expander. The library you want is probably "LiquidCrystal_I2C.zip":